1885.] NATURAL SCIENCES OP PHILADELPHIA. 391 



gain a security which only the development of flying carnivora 

 could overcome. The same may be said of tree-living and bur- 

 rowing animals. It seems highly probable that all these expedi- 

 ents were first adopted in the effort to escape destruction, and 

 that similar expedients were afterwards adopted by carnivora in 

 their pursuit of prey. It would not be safe to declare that the 

 various expedients mentioned were in every case first adopted 

 by food animals, and afterwards by the pursuing carnivora, but 

 the probability is that this was the case as a general rule. 



I may briefty l'efer to one other and a highly important result 

 of this evolutionary process. When powers of flight had become 

 balanced by powers of pursuit, it is evident that this expedient, 

 like that of armor, had lost its special utility. As a result another 

 and final expedient began a special development. Cunning and 

 shrewdness came into play as aids in escape. The mental powers 

 of animals began to strongly unfold. This was the case in both 

 classes of animals, and it is impossible to say which took the 

 lead. In both classes cunning, concealment, reasoning powers, 

 came into play, and blind flight and pursuit, or defense through 

 sheer bulk and strength, became succeeded, in many cases, by the 

 higher and more efficient agency of the mind. Instinct became 

 less dominant in animal life ; reason more dominant. In other 

 words, the mind grew more active and varied in its operations. 



The growth of this most recent animal modification is manifest 

 in the character of the later geological life. The development of 

 the brain becomes marked as we enter the tertiary era, and the 

 capacit}^ of the brain cavity steadily increases throughout this 

 era. What is called cephalization is the most important charac- 

 teristic of animal development throughout the tertiary age. In 

 the recent era this has reached its culmination, and mental 

 expedients have replaced physical conditions in the highest life 

 types as the most efficient agencies of attack and defense. 



Thus we seem to perceive four successive ideas emerging into 

 prominence in the development of the animal kingdom. In the 

 primeval epoch it is probable that only soft-bodied animals 

 existed, and the weapons of assault were the tentacle, the thread 

 cell, the sucking disk, and the like unindurated weapons. At a 

 later period armor became generally adopted for defense, and the 

 tooth became the most efficient weapon of attack. Still later 

 armor was discarded, and flight or concealment became the 



